A stone-edged causeway crosses the site's outer fosse on the east-north-east side, a deliberate and carefully made entrance feature, yet there is no corresponding gap in the earthen bank it leads to. Whatever arrangement once allowed people through has long since vanished, leaving a path that arrives at a wall with nowhere to go.

Ringforts, sometimes called raths, are among the most common archaeological monuments in Ireland, typically dating from the early medieval period, roughly 500 to 1000 AD. They functioned as enclosed farmsteads, the bank and fosse (a fosse being a defensive ditch dug around the outer perimeter) providing a degree of protection for a family and their livestock. This particular example at Tinnakilla sits in low-lying ground among mixed pasture and marshland, which is a less typical setting; most ringforts occupy drier, elevated ground. The enclosure is roughly circular, measuring 35.2 metres north to south and 36 metres east to west, with an earthen bank that stands 0.8 metres above the interior surface and 1.5 metres above the outer ground level. The fosse survives to a depth of 0.6 metres and a width of 1.45 metres along the northern to western arc, though elsewhere it has been lost beneath later field boundaries. The site was compiled and recorded by Denis Power, with notes uploaded in August 2011.

The enclosing bank is heavily overgrown with trees and bushes, which makes the circuit of the monument feel more enclosed than its modest dimensions might suggest. The interior slopes gently downward toward the centre, where the ground becomes rough and marshy, a reminder of the wet character of the surrounding landscape. Drainage on a site like this can make it awkward underfoot in wetter months, so visiting in a dry spell is sensible. The fosse, where it survives, is best observed along the northern and western edges before field boundaries interrupt it. The causeway at the ENE is the most legible feature on the ground, the stone edging still visible enough to follow, even if the bank it once served no longer offers any way through.